Crystalline bismuth-containing oxides

ABSTRACT

1. THE CRYSTALLINE BISMUTH-CONTAINING OXIDES OF THE FORMULA   BI2-XMXM&#39;&#39;2-3M&#34;YO7-Z   WHEREIN M IS A RARE EARTH METAL OF ATOMIC NUMBER 57-71, LEAD, CADMIUM OR YTRRIUM, M&#39;&#39; IS IRON GALLIUM, OR INDIUM, M&#34; IS ANTIMONY, TANTALUM, OR NIOBIUM, X IS A NUMBER IN THE RANGE 0 TO 1 Y IS A NUMBER IN THE RANGE 1 TO 1.5, AND Z IS A NUMBER IN THE RANGE 0 TO 0.5.

United States Patent O 3,847,829 CRYSTALLINE BISMUTH-CONTAINING OXIDES Robert J. Bouchard, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del. No Drawing. Filed Aug. 10, 1973, Ser. No. 387,479 Int. Cl. H01b 3/02 U.S. Cl. 252-635 10 Claims ABSTRACT OF THE DISCLOSURE Crystalline bismuth-containing oxides of the formula 2-x x 2y y 7z wherein:

have enhanced dielectric properties for use in capacitor applications.

BACKGROUND OF THE INVENTION (1) Field of the Invention This invention relates to a group of new crystalline bismuth-containing oxides having unexpected and unusual dielectric properties and their use in capacitor applications.

(2) Description of the Prior Art The mineral known as pyrochlore has a variable composition generally expressed as (Na,Ca) (Nb,Ti) (O,F) but which normally approaches the simpler formulation, NaCa-NbZOGF. The cubic unit cell of pyrochlore has dimensions of about 10.4 A. and contains 8 formula units of approximate composition AzBzXq, where A and B are cations in which the radius of A (i.e., Na+ or Ca is greater than that of B(i.e., Nb or Ti and where X is an anion (i.e., or F).

Numerous compositions, both natural and synthetic, crystallize with structures similar to that of pyrochlore. These are normally described as having crystalline structure of the pyrochlore-type. While pyrochlore-type compositions are generally of the formula A2B2X7, the seventh anion is not essential to the stability of the structure, and pyrochlore-type phases with compositions A2B Oq where Oszgl, frequently occur, e.g., Ag Sb O Vacancies can also occurs in the normally occupied cation positions particularly those of the large A cations. Crystalline composi tions of pyrochlore type can be obtained by combining r ions of different valencies in a number of Ways, e.g., 2+ A23+B24+O7, A2+A3+B4+B5+Q7 and I Multicomponent pyrochlore-type phases, such as positions which yield, upon firing, smooth resistors having a wide range of resistances, low temperature coefiicient of resistances and good stability properties. A component of these compositions are the oxides of the formula x 2-x) y Z-y) 7-2 wherein M is yttrium, lanthanum, thallium, indium, cadmium, lead or a rare earth metal of atomic number 58-71,

M is platinum, titanium, tin, chromium, rhodium, iridium,

rhenium, zirconium, antimony or germanium,

x is a number in the range 02,

y is a number in the range 0-2, and

z is a number in the range 0l, being at least equal to about x/ 2 when M is a divalent metal.

U.S. Pat. 3,681,262 to Bouchard discloses binary resistor compositions of polynary oxides and dielectric material. The polynary oxides are of the formula x 2x) y 2-y) 7-2 wherein:

M is Y, T1, In, Cd, Pb or a rare earth metal of atomic number 57-71;

M is Pt, Ti, Sn, Cr, Rh, Re, Zr, Sb or Ge;

M" is Ru or Ir;

x is a number in the range ()2;

y is a number in the range 0-2; and

z is a number in the range 0l, being at least equal to about x/ 2 when M is a divalent meta U.S. Patent 3,583,931 to Bouchard discloses electrically conductive compositions of the pyrochlore-related crystal structure of the formula (M Bi (M,,M ,,)O wherein:

M is yttrium, thallium, indium, cadmium, lead or a rare earth metal of atomic number 57-71,

M is platinum, titanium, chromium, rhodium or antimony;

M" is ruthenium or iridium;

x is a number in the range 01;

y is a number in the range 0 to about 0.5, with the proviso that y is a number in the range 0-1 when M is rhodium or more than one of platinum, titanium, chromium, rhodium and antimony; and

z is a number in the range 01, being at least equal to about x/2 when M is divalent lead or cadmium.

In Kristallografiya, 10(2), 246 (1965), Kupriyanov et al., in an article entitled New Pb and Bi Containing Pyrochlores, discuss anion deficient pyrochlores of the type Bi M+ M+ O wherein M+ is cadmium and M+ is tin or zirconium.

SUMMARY OF THE INVENTION In accordance with the present invention crystalline bismuth-containing oxides having enhanced dielectric properties have been discovered which are of the formula 'Bi M M' M" 0 wherein:

M is a rare earth metal of atomic number 57-71, lead,

cadmium or yttrium,

M is iron, gallium, or indium,

M" is antimony, tantalum, or niobium,

x is a number in the range 01,

y is a number in the range 14.5, and

z is a number in the range 0-0.5.

The crystalline bismuth-containing oxides of this invention are distinguished from pyrochlore-type oxides of is at least 0.5, Bi is at least 1 and O is at least 6.5

DETAILED DESCRIPTION OF THE INVENTION This bismuth-containing oxides of this invention possess crystal structures that are closely related to that wherein M is iron or indium, and M" is antimony or niobium.

The oxides of the present invention may be prepared by grinding reagent grade oxides in an automatic mortar grinder using an agate mortar and pestle. Reaction of the mixture of the requisite ground oxides is then aifected by heating the mixture either under vacuum, or in oxygen or air, to a temperature in the range of about 800-l300 C. Optionally, an excess of Bi O over that required for stoichiometry can be used to promote faster reaction and to facilitate the preparation of pure products. The excess B1 0 can be leached out of the crude product with a suitable solvent such as nitric acid.

Prior to 'heating, the mixture of oxides may be in compacted (pelletized) or uncompacted form, as desired.

Generally capacitor dielectrics tall into two categories: the first has a relatively temperature-independent dielectric constant, but the value of the dielectric constant is very low (5-10). Such materials as electrical porcelain and mic-a fall into this class. The second category includes materials like BlTlOg, which have very high dielectric constants l000), which is desirable, but they are extremely temperature dependent, which makes them useless as circuit elements in tuning or resonance circuits, since small normally unavoidable changes in ambient temperature throw the circuit out of resonance.

The compositions of the present invention are useful over a wide range of frequencies. Table 2 illustrates the invariance of the dielectric constant with varying fro.- quencies of the compounds listed in Table 1. In Table 2 all dielectric measurements were made on sintered disks of the compounds using silver point electrodes and an automatic capacitance bridge with digital circuitry at C.

TABLE 2-]? RE QUENCY INVA RIANCE Compound formula K D F K D F K D F K D F BltFeSbOr 39.7 .0001 39.8 .0007 39.7 .0005 39 8 .003 Bi2InSbO1 28.1 .008 27.9 008 27.5 004 27 5 .006 BlPbFeu.sSbi.iO1 15.5 .004 15.5 .002 15.5 .001 15 5 .002 BrPbFcSbOM 49 .006 49 .006 48.5 .004 48 5 .005 B12F8Nb07 144 .005 144 002 144 .001 144 .001

It is preferred to effect the reaction in platinum crucibles open to the air, or under oxygen, or in sealed platinum tubes under vacuum. Vessels of other high-melting inert materials such as mullite (3A'l O -2SiO Vycor, alu- 4O mina, gold, and the like, may also be used.

Many of the compounds of the present invention can 'be grown in the form of single crystals. The size of the single crystals obtained can be increased easily using techniques known in the art, i.e., increasing the flux/oxide high dielectric constant, for example above about 15,

which is relatively independent of temperature. Table 1 illustrates the temperature dependence of the dielectric constant of a wide range of compounds typifying the present invention. Samples A, B and C have dielectric constants which are essentially independent of temperat-ure. Sample D has a positive temperature dependence, while Sample E has a negative temperature dependence. Compounds having a negative temperature dependence are useful for certain consumer electric applications. The

dielectric measurements given in Table 1 were made on sintered disks of the compounds using silver point electrodes and an automatic capacitance bridge with digital circuitry.

The compositions of this invention are also useful for screen-printable dielectric applications. A requirement for this application is that the material, after printing in a pattern through a screen, sinters to a dense, adherent film under firing conditions commonly employed in the thick film industry, i.e., belt furnaces with top temperatures in the 1000-1050 C. range. It is somewhat unusual to find a material which has these properties, especially without the addition of any low-melting binders. For example, BaTiO dielectric has to be fired at temperatures greater than 1200 C. to achieve sintering, so it is completely unsuitable for screen-printing applications.

Although the bismuth-containing oxides of this invention sinter very readily, it is occasionally desirable to add a small amount of glass to raise the fired density of a sintered piece or to improve adherence of a screen-printed film to a substrate where this is a particularly important requirement. Such additions fall within the scope of the invention.

Optionally, the addition of a third component to the bismuth-containing oxide and glass composition sometimes improves one of the dielectric proper-ties. The effects of adding glass and Ca'IiO to Bi FeNbO are shown in Table 3. Dielectric compositions containing CaTiO are described by R. Amin in US. Application Ser. No. 291,- 174, filed Aug. 22, 1972, now US. Pat. 3,787,219.

TABLE l.-TEMPERATURE INVARIANOE Dielectric constant, K (T in 0.)

Loss dissipation factor, DF (T in C.)

Compound Fre Sample formula (Hz. (T (T2) (T (T A BizFeSbO7 10 38 40 .004 (100) .003 +125) B... Bi InSbO 10 28 (+25) 29 (+400) .008 (+25) .01 +400) 0--.- BiPbFeo.nSbi.s01 10 15.5 (196) 15.5 (+25) .001 (196) .004 (+25; D BiPbFeSbOM 10a 42 (196) 49 (+25) .066 (196) .006 (+25 E BizFBNbO7 10 146 (0) 134 125) .001 (0) .004 (+125) *K and DF were measured on sintered pellets at a frequency of 10" Hz "T is temperature coefficient of capacitance calculated by the equation:

TCC=C at Tr-C at T2X10 C at T1 (AT) Table 3 shows that the addition of glass improves the loss factor, but also lowers the dielectric constant and temperature coefficient of capacitance. However, where the loss dissipation factor is very important for a particnlanapplication, the over-all performance may be improved. The Table also shows that the addition of glass plus CaTiO (which also has a negative temperature coefficient and high dielectric constant, but is very high melting and therefore not sinterable under the usual available firing temperature of 1000 C.) can drastically lower the loss factor while retaining a high temperature coefficient, although dielectric constant is still lowered over the value obtained for Bi FeNbO Therefore, it will be apparent to those skilled in the art that the addition of small amounts of various components to the compounds of this invention can modify the dielectric properties so as to fine tune these properties to match the requirements for a particular application. Such modifications are Within the scope of this invention.

11 EXAMPLES OF THE INVENTION 'The following examples, illustrating the novel compositions of this invention and the method of preparing them, are given without any intention that the invention belimited thereto. Unless otherwise noted, the subject oxides were all prepared by grinding the reagent grade starting materials in'an automatic mortar grinder using an agate mortar and pestle. All percentages are by weight.

. .Example 1-Bi GaNbO 0.9319 g. of Bi O 0.1874 g. of Ga O and 0.2658 g. of Nb O were ground together for 1 hour, sealed in a Pt tube under vacuum and fired to 1300 C. for approximately 16 hours. The product was a yellow mass which gave an X-ray pattern characteristic of a pyrochlore with a (Lattice parameter) 10.45 A.

Example 2-Bi FeNbO 1.0251 g. Bi O 0.1757 g. Fe O and 0.2924 g. Nb 0 were ground together for 30 minutes, pressed into a pellet, sealed in Pt under vacuum, and fired at 1000 C. for 48 hours. The red-brown product had an X-ray pattern of the pyrochlore type, a 10.50 A.

Example 3Bi InSbO-;

0.9319 g. Bi O 0.2776 g. In O and 0.3235 g. Sb O were ground together for one hour, pressed into a pellet, sealed in Pt under vacuum, and fired to 1000" C. for 16 hours. The yellowish-white product had an X-ray pattern of the pyrochlore type, a,,==10.69 A. with several weak extra lines.

Example 4-'-Bi InSbO 6 Example 5Bi FeTaO 0.9319 g. Bi 0 0.1597 g. Fe O and 0.4419 g. Ta O were ground for one hour, pressed into a pellet, and fired in air in a Pt crucible t0 1100 C. for 24 hours. The brown product had an X-ray pattern of the pryrochlore type, a =10.50 A.

Example 6Bi GaSbO-;

4.0072 g. Bi O 0.8060 g. Ga O and 1.2534 g. Sb O were ground together for one hour, pressed into a pellet, fired to 1000 C. in air in a Pt crucible for 72 hours. The tan product had an X-ray pattern predominantly of the pyrochlore type, a 10.38 A.

Example 7-Bi GaTaO 0.9319 g. Bi O 0.1874 g. Ga O and 0.4419 g. Ta O were ground together for one hour, pressed into a pellet, fired to 1200 C. in air in a Pt crucible for 16 hours. The yellowish-white product had an X-ray pattern of the pyrochlore type, a =10.43 A.

Example 8BiCdFeSbO 0.3281 g. CdO, 0.5954 g. Bi O 0.2040 g. Fe O and 0.3724 g. Sb O were ground together for 30 minutes, and fired in air to 1000" C. in a Pt crucible for 16 hours. The brown product had an X-ray pattern of the pyrochlore type, a,,: 10.33 A.

0.4685 g. PbO, 0.4890 g. Bi O 0.0837 g. Fe O and 0.4588 g. Sb O were ground together for 30 minutes, and fired in air to 1000" C. in a Pt crucible for 16 hours. The yellowish-brown product had an X-ray pattern of the pyrochlore type, a 10.43 A.

Example 10-BiPbFeSbO 0.4910 g. PbO, 0.5126 g. Bi O 0.1757 g. Fe 0 and 0.3207 g. Sb O were ground together for 30 minutes,, and fired in air to 1000" C. in a Pt crucible for 16 hours. The yellow-brown product had an X-ray pattern of the pyrochlore type, a 10.44 A.

Example 11BiGdFeSbO 0.5666 g. Gd O 0.7283 g. Bi O 0.2496 g. Fe O andv 0.4556 g. Sb O were ground together for 30 minutes, and fired to 1100 C. in a Pt crucible in air for four hours. The orange-brown product had an X-ray pattern of the pyrochlore type, a,,=10.37 A.

Example 12BiYFeSbO g. Y203, g. Bi203, g. F6203, and 0.3824 g. Sb O were ground together for 30 minutes and fired in air for four hours at 1100 C. in a Pt crucible. The orange-brown product had an X-ray pattern of the pyrochlore type, a =10.32 A.

Example l3-BiLaFeSbO 0.5438 g. i 0 0.3927 g. Gd O and 0.5639 g. FeSbSOB were ground together for 30 min., pressed, sealed in platinum under air, and fired to 1200" C. for 16 hrs. The hard brownish-white product had an X-ray pattern of the pyrochlore type, a =10.50 A.

Example 14BiGdFeSbO 0.5438 g. Bi O 0.3927 g. Gd O and 0.5639 g. FeSbO were ground together for 30 min., pressed, sealed in platinum under air, and fired to 1200 C. for 16 hrs. The hard, brownish-white product had an X-ray pattern of the pyrochlore type, a =l0.43 A.

Example 15Bi FeSbO This example illustrates the preparation of Bi FeSbO in the form of single crystals. 0.3992 g. Fe O 0.7287 g. Sb O and 13.9788 g. Bi O were ground together for 30 minutes, fired to 1200 C. for 16 hours in an open Example 16 The compounds listed in Table 4 were mixed with 20% by weight of an organic vehicle composed of 10% ethyl cellulose in ,B-terpineol. This mixture was screen-printed onto 96% alumina substrates over Pd/Ag electrodes, dried, reprinted, dried, then second electrodes were printed on. This composite was fired to various temperatures for 10 minutes, cooled and the dielectric properties measured on a GR automatic bridge. The average film thickness was about 0.002 in.

TABLE 4.-EFFEOT OF FIRING TEMPERATURE Firing Dielectric Loss temperaconstant, dissipation Compound formula ture, C. K factor, DF

Bi2FeSb0 950 32. 024 BigInSbO-r- 850 23. 7 0006 BizInSbO 900 24. 6 0007 Bi2InSbO1 950 24. 7 0004 BizInSbO 1, 000 28. 9 0007 1, 050 40. 6 0001 BizInSbO1 Four capacitor fabricates using the screen-printed films prepared as described above, were fired at each temperature given in Table 4. The average dielectric properties obtained at 10 Hz. are recorded in the Table. It can be seen from the data that while the best samples are the ones fired at the highest temperatures, useful values of dielectric constant and dissipation factor are obtained over a wide range of firing temperatures.

Although the invention has been described and exemplified by way of specific embodiments, it is not intended that it be limited thereto. As will be apparent to those skilled in the art, numerous modifications and variations of these embodiments can be made without departing from the spirit of the invention or the scope of the following claims.

I claim:

1. The crystalline bismuth-containing oxides of the formula wherein M is a rare earth metal of atomic number 57-11, lead,

cadmium or ytrrium, M' is iron, gallium, or indium, M" is antimony, tantalum, or niobium, x is a number in the range 0 to 1, y is a number in the range 1 to 1.5, and z is a number in the range 0 to 0.5 I y 2. The crystalline bismuth-containing 'oxides of Claim 1 in which M is iron. 3. The crystalline bismuth-containing oxides of Claim 2 of the formula Bi FeM"O wherein M is antimony or niobium. J 1* F Y 4. The crystallinebismuth-containing oxide of Claim-2 of the formula 1 a 1 I A, Bi FeSbO .7 h 5. The crystalline bismuth-containing oxideof Claim) of the formula I Bi FeNbo 6. The crystalline bismuth-containing oxides oftClairn 1 of the formula Bi M'M"O wherein I M is iron or indium and I v M is antimony or niobium.

7. The crystalline bismuth-'containingoxide of Claim 6 of the formula Bi InSbO 8. A single crystal of acompound of Claiml.

9. A single crystal of a compound of Claim 4.

10. In the method of screen printing dielectrics by printing a dielectric material in a pattern throughla screen and sintering the dielectric material to a dense adherent.

film, the improvement which comprises using a-crystalline bismuth-containing oxide of Claim '1 as the dielec-' tric material.

References Cited v US. c1 X.R., h v, 2s2 s19; 423-594, 617; 117-212; 317 2ss UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 7,829

DATED November 12, 1974 INVENTOR(S) Robert J. Bouchard It is certified that error appears in the above-identified patent and that said Letters Patent 7 are hereby corrected as shown below:

Column 1, line 53, "occurs" should read -occur-.

Columns 3 and 4, Table l, the entry in the line for Sample E under the heading "Dielectric constant, K'" in the colunm designated as (T should read -l34 (+l25)-.

I Column 5, Table 3, the heading "K' at 25C." should read K' at 25c.*-,

Column 5, Table 3-, line I 5, the first entry under the column "TCC**" should read -'62 5.

Column 5, line 10, the equation should read C at T -C at T2 C at T (AT) Column 6, line 57, should read --O.5482 g. Bi O 0.3833 g. La 0 and 0.5685 g. FeSbO Signed and Salad this Twenty-first Day Of December 1976 [SEAL] A I 188 I.

RUTH C. MASON C. MARSHALL DANN Arresting Officer v Commissioner ujPalenrs and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,847,829

DATED November 12, 1974 INVENTOR(S) Robert J. Bouchard It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: 1

Column 1, line 53, "occurs" should read -occur-.

Columns 3 and 4, Table l, the entry in the line for Sample E under the heading "Dielectric constant; K'" in' the column designated as (T should read -l34 (+l25)---.

Column 5, Table 3, the heading "K' at 25C." should read -K' at 25C.*-.

Column 5, Table 3, line5, the-first entry under the column "TCC**" should read -'-,625-.

Column 5, line 10, the equation should read c at T -C at T2 0 at T (AT) Column 6, line 57, should read --o.54s2 g. Bi O 0.3833 g. La O and 0.5685 g. FeSbO Signed and Scaled this Twenty-first D8) Of December 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ufParenrs and Trademarks 

1. THE CRYSTALLINE BISMUTH-CONTAINING OXIDES OF THE FORMULA 